This invention relates to the use of amphiphiles for permanently improving the dye compatibility of polyolefin-based moldings, fibers and films.
In many cases, the surface of plastic products has to be provided with three-dimensional, color or other effects which either can only be produced in completely, if at all, during the forming process for technical reasons or can only be inelegantly produced for economic reasons.
This applies, for example, to the dyeing and printing of the surfaces of polyolefin-based moldings, fibers and films. On account of their non-polar character, high molecular weight hydrocarbons, such as polyethylene or polypropylene, have a low surface tension (typically of the order of 20 to 30.times.10.sup.-5 Ncm.sup.-1. The adhesion of printing inks and dyes to their surface is correspondingly weak (typically below 0.5 Nmm.sup.-2).
It is known from the prior art that the compatibility of plastic surfaces with can be improved, for example, by oxidative aftertreatment processes, such as corona or plasma treatment. In processes such as these, the surface of the plastic is oxidized or chemically modified in the presence of gases and discharges, so that certain surface properties of the plastic can be modified. However, apart from their high energy consumption, processes such as these always involve an additional step and lead to ozone emissions in the manufacture of plastic parts.
Chemical pretreatment processes, including for example treatment with fluorine or chlorine gas, with chromosulfuric acid or fluorosulfonic acid, etc., have also been known for some time.
In addition, special substances which were applied to the surface of the plastic to make the problematical dyeability of polyolefins more favorable were known from the earlier literature.
Thus, even U.S. Pat. No. 3,284,428 points out the dyes adhere very poorly to polyolefin fibers because the polyolefins have an inert surface. It is also pointed out that although polypropylene, for example, can be dyed, the dye absorption rate is far too low for industrial technical requirements. U.S. Pat. No. 3,284,428 proposes the use of nickel derivatives of special diamines to solve this problem.
U.S. Pat. No. 3,424,716 describes polyolefins to which ternary mixtures of nickel compounds, sulfo compounds and n-octylphenyl salicylate are added as additives in order to improve the dyeability and stability of the polyolefins.
EP-B-372 890 describes polyolefin- or polyester-based fibers with a lubricant applied to their surface. This lubricant comprises a mixture of (1) fatty acid diethanolamide, (2) a polyether-modified silicone, (3) a sorbitan fatty acid ester and (4) a metal salt of an alkyl sulfonate. Components (1) to (4) are present in special quantity ratios. According to page 3, lines 20 to 26, the mixture of components (1) to (4) is applied to the surface. The technique by which the mixture containing the four components is applied to the surface of fibers is described in detail on page 4, lines 6 to 9. The application techniques mentioned include a) the use of rollers, b) spraying and c) immersion. Accordingly, the process according to EP-B-372 890 is a process in which a mixture of components (1) to (4) is applied to the surface of polyolefin moldings in an additional processing step. Accordingly, the expression "applied to the fiber surface" used in claim 1 of EP-B-372 890 may be clearly interpreted by the expert to mean that any adhesion involved is loose and temporary, for example in the form of relatively weak adhesion forces, and cannot in any way to be considered to represent permanent anchorage.
Even the more recent literature (both patent documents and scientific publications) that the dyeability of polyolefins is extremely problematical. For example, EP-B-595 408 describes a process for improving the surface compatibility properties of polypropylene which comprises heat-treating polypropylene together with at least one olefin compound polybrominated at an aromatic ring in the absence of free radical initiators.
U.S. Pat. No. 5,045,387 describes the treatment of polyolefin-based fibers or films in which special polyalkoxylated polydimethyl siloxanes or alkoxylated ricinoleic acid derivatives are applied to the surface.
In a fairly recent Article, J. Akrman and J. Prikryl investigate the dyeing behavior of polypropylene fibers (cf. Journal of Applied Polymer Science 1996, Vol. 62, pages 235-245). The authors of this Article point out that the causes behind the poor dyeability of polypropylene have been known for some time and lie in the fact that the material has high crystallinity and an extremely non-polar aliphatic structure which does not contain any reactive sites. The authors also point out that although additives containing basic nitrogen are known from the prior art, no seriously commercial product which satisfactorily solves the dyeability problems is available to the expert despite the intensive research efforts in this field. The authors then report--on the basis of their own studies--that a polypropylene fiber dyeable in acidic medium can be obtained by adding a special high molecular weight additive containing basic nitrogen on a rigid polymer chain to the polymer before it is extruded.
In view of the very widely used traditional chemical aftertreatment processes, such as corona and plasma treatment, it is known to the expert that no exact statements can be made as to the various processes involved. However, it has been established that oxidative surface changes occur and result in the formation of certain "active centers". However, their concentration generally decreases with time so that the pretreatment effect also is only in evidence for a certain time, generally not more than 72 hours (cf. for example, Klaus Stoeckert (Editor), "Veredein von Kunststoff-Oberflachen", Munich 1974, page 137).
One feature common to all the known processes is that, in general, the desired surface effects are only temporarily present.
EP-B-616 622 relates to extrudable compostable polymer compositions comprising an extrudable thermoplastic polymer, copolymer or mixtures thereof containing a degradation-promoting system of an auto-oxidative component and a transition metal. The auto-oxidative system comprises a fatty acid, a substituted fatty acid or derivatives or mixtures thereof, the fatty acid having 10 to 22 carbon atoms and containing at least 0.1% by weight of unsaturated compounds and at least 0.1% by weight of free acid. The transition metal is present in the composition in the form of a salt in a quantity of 5 to 500 ppm and is selected from the group consisting of cobalt, manganese, copper, cerium, vanadium and iron. The composition is said to be oxidatively degradable to a brittle material in the form of a film around 100 microns thick over a period of 14 days at 60.degree. C. and at a relative air humidity of at least 80%.